Timing of Nest Relief and Its Effect on Breeding Success in Adelie Penguins (Pygoscelis adeliae)

I determined the fates of 259 eggs laid by 130 pairs of banded Adelie Penguins (Pygoscelis adeliae) at Cape Bird, Antarctica (77°13′10″S, 166°28′30″E). Failure of penguins to return from feeding at sea in time to relieve their mates at the nest resulted in the desertion of 48 eggs (47.5% of all egg losses) and the starvation of 29 chicks (35.4% of all chick losses). Eggs were more likely to be deserted if they belonged to parents that had bred either very early or very late. Most eggs were deserted when females did not return in time to relieve their mates from the First Incubation Spell, so that the risk of desertion became appreciable only after the eggs were 16 days old. Starvation was especially likely when chicks were 6-8 days old, largely because males did not return to relieve the females, particularly from the Second Incubation Spell. Pairs that successfully completed nest relief regulated the total duration of the First and Second Incubation Spells, keeping it slightly less than the duration of the incubation period.